Size reduction apparatus



1957 P. H. SPITZ ET AL SIZE REDUCTION APPARATUS 2 Shets-Sheet 1 Filed July 15, 1954 FLU+E GAS BURNER COKE AIR um R SI. P0 w s a T 5 N N R ERE O mum w -28 A PD/m Y B NAPHTHA RESIDUUM Jan. 8, 1957 P. H. SPITZ ET AL 2,776,799

SIZE REDUCTION APPARATUS Filed July 15, l954 2 Sheets-Sheet 2 HANDWHEEL TARGET POSITION INDICATOR INVENTORS PETER H. SPITZ DANIEL S. BOREY ATTORN EY United States Patent"- S REDUCTION-APPARATUS.

Peter; IL; Spi t z NeWpYork, N.-.Y., audwDanieL S.-; Borey,

Cranford, N. L, assignors to Essa-Research and Engiueering .Compauya. corporation' of. Delaware Application July' -15, H54, Serial No. 443,494

3 Claims. (Cl,.24.1m40).

This invention pertains to an improved hydrocarbon oillifluid coking process. .The presentinyention also re,- lates to an apparatus and to .a process for the comminution of particulate solids; More particularly, this invention isconcerned With'the preparation of seedicokeiin a hydrocarbon oil fluid coking system. The present invention involves apparatus for the size reduction of heatcarryin'g so'lid'particles used in fluid coking processes and also .involvesa particular processing arrangement for seed coke production, characterized by its practicability and efli'ciency.

A coking process for pyrolytically upgrading petroleum oils, which'utilizes the fiuidized'solids technique has been recentlydevelopedj Inthis' fluid coking process, as is knownby the art, a mass of fluidized high'temperature solids such as sand, metal'particle's, spent catalyst etc. and especially coke particles formed in, the process, is used to supply the heat for conve t n O A charging stock-to be upgraded is sprayed into the fluid bed and, upon contact with the high temperature .solid's, undergoes pyrolysis; evolving lighter hydrocarbon vapors and depositing, carbonaceous residue, i. e.,,coke, on.the, solids. Various solids ,such' as thosementioned above may be used'to supply the heat to conversion. However, since coke is a product of the process, this'petroleum coke is the preferred contact solids;

Because of the deposition of coke, on the particles, the particles increase in size and steps mustrbe taken to counteract this growth; The present invention pertains particularly to a means and a method for controlling the number, the particle size and particle .sizedistributionpf the circulating solids, whereby continuous and efficient operation of the. coking. process is assured.

Charging stocks customarily used in fluid coking operations comprise petroleum tars, cycle stocks, vacuumand atmospheric. residua, recycle heavy ends from the coker effluent, and similar high-boiling lowv value, heavy oils containing constituents non-.yaporizable without thermal cracking. Broadly, howeyencharging stocks suitable'for use in a fluid coking process include shale oils, asphaltsl, tars, coal tars, synthetic oils, extracts, cycle stocks, whole crudes, distillate and residual fractions therefrom, or mixtures thereof. I

In most fluidized -solids-systems wherein a solid 'is reacted or contacted with a fluid, the solid is usually circulated to an external vessel forregenerative orreheating purposes In such multi-vesselsystems, the necessary driving force for. circulating the solids. may be created by use of:apressurizing,standpipe. In such a standpipe,sthe solids are conveyed downwardly-at relativelyhighzdensitiesuntil a suff cient fluistatic head is created-.to convey the solids. This invention has particular relationshipto a.:fiuid coking,. system .of this. nature wherein ,the. heat- ,carrying .solidsuare circulated ,fromthe coking vessel, to. a heatingflv-essehand back through a pressurizing standpipe system.

In fluidized solids systems, it is highly desirable, if 'not necessary, to maintain an optimum size-and size distribu- 2 tion of the fluidizedgsolidsg If: the solids are too finqthe solids are readily lost from the system by entrainment-in the fiuidizing gases; If the solids are too large, fluidizetion becomes 'difiicult; particularly Within the range of fluidizing gas velocities us'ed and proper circulation ofthe solidsis hindered. In hydrocarbon oil fluid coking systems, it is preferred to operate with particles in the-size range of aboutAQ-SOOunicro-ns, although the. size of the particles may vary somewhat beyond these limits.

Because of .the above-mentioned accretion inthe size ofthe-particles, portions of the coke must be. withdrawn from a fluid coking system to maintain .the total mass or weight inventory of the solids'substantially. constant and small size particles must be supplied to the system to keep the numerical inventory. of the particles in,the system substantially constant. Preferably this. withdrawal and addition is donecontinuously; Experience indicates that the, desirable seedgcoke size is' Within the range of I to 200 mesh. Below this range, particles agglomerate readily and/or are. blown from the system and. above this-range the amount of material thatmust be passed through the grinding device, to maintain a numerical balance of particles inthe coking system becomes prohibitive. i V

The prior art has suggested the, use of jet attriters or impact 'grindersto obtain the. necessary seed coke production in fluid coking processes. i

The jet; attrition grinders or impact grinders known by the prior art operate on the principle of accelerating coke particles, with" a fluid medium, e. g, steam,.to a, high velocity and discharging thernixture againsta stationary target. The impact with'the target shatters the particles and yields the desired size reduction. To attain the, high velocities necessary for satisfactory grinding static pressure energy is convertedinto kineticenergy. It-is, therefore, desirable, to provide for the maximum pressure drop over the jet grinding means within the limits allowed by the process. v v

The design of the jet attrition apparatus has presented problems. One of the main problems ,has been rapid erosion of .the target surfaces, Another problem is the efhcient design of tlrejtarget surface such that the maximumimpacting of the particles isobtained. This invention by a particular jet attriter design admirably solves these problems.

It is, therefore, an object of the, present invention to devise a process and apparatus for the comminution of particulate solids; particularly of, coke particles, used in hydrocarbon oilfl'uid coking systems. Another object is torpr ovide seed coke as growth nuclei in ,a hydrocarbon oil fluid coking system by jet or impactgrinding,

A salient feature and object ofgthis inventiouis to incorporate a jet grinder means within a fluid coking system that makes maximum use of'ythe static pressure differential available. To do this, particulate coke to be reduced in size is withdrawn from the lowermost portion of one of the pressurizing standpipes, as atthis point the coke is under the highest static pressure existing, within the process. Afterbeing reduced in size,.. the impacted coke is returned 'to the system to a point having the lowest static pressure. Preferably the coke is returned to the coking ,vessel; above the fluidized bed of. solids contained therein. This place of return has a relatively low staticflpressilre and also is chosen for reasons stated below.

One of the problems in fluid coking, and in the provision of seed coke, therefore, is the loss of fines from the system. As the fluidizing gas passes through the bed of solids, the smaller particles are entrained] therefrom and will be lost in the system through the vented jgases, particularly with the burner flue gases.- This is unde- -sirabl'e,not only "because these fines are valuable as seeds,

but also because such losses contribute to atmospheric pollution. By introducing the seed coke into the coking reactor in accordance with this invention, this loss is avoided. The fines are agglomerated on the wet coke particles in the reactor bed and thus are held in the system. Any fines entrained through the reactor cyclones are returned with the stream of recycled heavy ends in a wetted condition.

The nature and objects of this invention will be more fully understood by reference to the attached drawings which form a part of the specification. In the drawings, Figure I diagrammatically portrays a fluid coking system operated in accordance with the teachings of this invention. Figure II illustrates a preferred jet impact grinder used for the production of seed coke. Figure III is a cross-sectional view of the apparatus shown in Figure 11 taken along line III-J11 of Figure II.

In brief compass, the present invention proposes an improved hydrocarbon oil fluid coking process which comprises injecting a charging stock into a fluidized bed of particulate solids maintained at a coking temperature in a coking zone to form relatively lighterhydrocarbon vapors and carbonaceous residue which is deposited on the solids causing them to grow in size, withdrawing the vapors overhead as product, withdrawing as product portions of the particulate solids at a rate adjusted to maintain the mass of the solids in the process substantially constant, circulating the particulate solids to an external heating zone and back to maintain the coking temperature, withdrawing a portion of the solids so circulated at a point of relatively high pressure and impelling the withdrawn portion at a relatively high velocity against an impact surface to produce small particles of seed size, and introducing the particles so impacted into the upper portion of the coking zone above the fluidized bed whereby the particle size, particle size distribution and number of the particulate solids in the process are maintained substantially uniformly.

In a preferred embodiment of this invention, the comminution of the solids is accomplished by use of size reduction apparatus of special design which comprises an attriter vessel adapted to contain a moveable target and having an outlet at one end for the discharge of the comminuted coke, a target positioned within the vessel, an acceleration conduit for admitting a high velocity coke-gas suspension into the vessel in the form of a confined stream, the acceleration conduit being radially positioned on the vessel and terminating in spaced relation ship to the target, positioning means operatively connected to the target for positioning the target transversely to the acceleration conduit, and mounting means for detachably mounting the positioning means on the other end of the vessel. Preferably the target is an elongated channehshaped member positioned in such a manner that the confined, high velocity, solids-gas stream strikes substantially perpendicularly the inner bottom of the channel-shaped member.

Referring to Figure I, there is shown schematically a coking process incorporating the teachings of this invention. The art of fluid coking of petroleum oils is generally quite well known and for this reason will be but briefly described, sufficient to create a setting for this invention. The major items of equipment shown in the drawing are a fluid coking vessel 1 with a superposed product quench and separation system, a heating vessel 2 or fluid bed burner, and a jet attriter 3.

An oil to be converted, such, as a heavy vacuum residuum, is introduced into the coking vessel by lines 4. A fluid bed of particulate petroleum coke is maintained in the vessel at a temperature in the range of 900 to 1600 F. The residuum is converted to lighter vapors which pass upwardly through cyclone system 5 wherein entrained solids are removed and thence into the quenching and fractionation section of the coker. The vapors issuin; om the cyclone system are cooled by descending liquid to substantially stop further reaction and to con dense heavy impurity containing ends. The condensed ends are removed from the tower by line 6, a portion of which are recycled by line 7 to the coker, and another portion is recycled by line 8 through heat exchanger 9 to serve as a quench medium or reflux. The vapors continue upwardly through the tower and further amounts are condensed out. A gas oil portion of the vapor is removed by line 10 as product. A portion of this gas oil is recycled by lines 11 and 12 through heat exchangers l3 and 1 t respectively to serve as reflux and to affect staged heat removal. The remaining lighter portions of the coker products are removed overhead by line 15 as product. The coker products can, of course, be subjected to further treatment as desired, e. g., hydroforming, stabilization, blending, catalytic cracking, etc.

Steam or other fluidizing gas is admitted to the base of the coker as by line 16 and serves to strip the coke particles before they are circulated to the heater and then serves to fluidize the solids contained in the coker. Large size particles or agglomerates may be formed in the coker and these oversize particles can be removed by line 17.

To maintain the coking temperature, a portion of the coke is continuously circulated through line 18 to an external heating zone, e. g., a fluid bed burner 2, wherein it is reheated to a temperature of about to 300 F. above the coking temperature. The reheated coke is then circulated to the coking vessel from the burner by line 19. The circulated coke descends downwardly through a standpipe in a relatively dense phase condition whereby a fluistatic head is created that serves as a driving force and a pressure seal between the vessels, as is well known by the art. Air or another oxidizing gas is admitted to the base of the burner vessel by line 20. This air serves to fluidize the coke therein and supports a partial combustion of the coke. The flue gases formed by the combustion, after having entrained solids substantially removed, are vented overhead from the burner vessel by line 21. Other heating means may, of course, be used to heat the coke including transfer line burners, gravitating bed burners, shot-heating systems, or other direct or indirect heating means.

A net amount of coke beyond that required to supply the necessary heat for the pyrolysis is produced by the process. This coke can be removed as product from the process by line 22. Preferably, this coke is quenched to prevent ignition of it upon contact with the atmosphere. Also preferably, the coke removed as product is elutriated or otherwise classified so that only relatively coarse coke is removed as product. This practice reduces greatly the amount of grinding or size reduction that must be practiced to provide seed coke for the process.

The above-described fluid coking system is exemplary of one in which the present invention has applicability. There is no intent to claim features of fluid coking other than those that necessarily relate to the present invention.

To produce growth nuclei or seed coke, coke is withdrawn from the cold coke standpipe 18 by line 23 and is circulated to the jet attriter. It is preferred to withdraw the attriter feed from the cold coke standpipe in this particular coking process because the pressure at this point exists primarily because of a fluid bed and is relatively constant. A small amount of steam or other aeration gas may be admitted to line 23 by line 24, to facilitate the flow of the coke. The coke is admitted from line 23 into line 25 wherein it is admixed with substantial quantities of a conveying gas, e. g., steam, that serves to accelerate it to a high velocity suflicient to create the kinetic energy necessary for the grinding. The contents of line 25 are then discharged into attriter vessel 3 wherein the high velocity particles are impacted against a target and comminuted. The

aopenationrofiattriter vessels3: isnnorezffillynpresentedshereinafter;

:Thecoutlet velocities zuse'd .in the. jets gninderqwill, a-of ccourse, vary with such 1 factors as acceleration :tube

ndiametereand length, :solidsiloadingxtarget configuration,

--i3itld rparlticularly whet-available :pressure rzdrop racross tthergrinder. i' llhergas':velocitiescat? the *outletwmay :range :from.Yi2001.to2,000 ft;/ sec. with '-velocities inthe range lnfL ZOO to I 7 r'ftjsec. i'b'eing normal and thei'maximum welo'cityrofithmsolids :may: range: from 5010 110.001 ft./sec.

be blown out of the-burner and lost from the system.

Steam or :r'other' "purge agas may beconneoted to -line 26- by *line 27; 'Ihis gas *will not necessarily be adunitted thmugh this connection' during normal operation. During periods whem the attr-iter -is not operating; it: is

Wessel to -prevent coke 'deposition on the' terminating portions of=-line' 26. I

I *It is advantageous in some: applications ofs'ithis invention= =to: elutriate: or:otherwise'lclassifylthezmaterial'withdrawvn trom the I coke :circulation systemcpriorrtoagrindj:

i-dng iit. #:Statcdx iiifierently, Fit-2 may: ber fdesi re'd torigrind aonlyaa 'relativejlyccoarse rn'atenialsand to-aauoidstunnecess sary: handling 1? of; the :material alread'y *xin rith'ettklesired size range. Thus the contents of line 23 maysbexelutri- :zated1orcotherwisecclassifiedrsoithat onlyirelatively coarse;

umaterialris .passedttonjeti=atti itern3t,

It is also advantageous to providerzmeanszfore creating 1: amlarger l-PlfiSSIllI6 ..:diiferential overzrthe mjetaattriter vesseliithansthatcexistingtinherently in the; process; :Eor sexample,fiansiaspirationi Systemgin e;, la; steam. t-: ejector, *may' =berinsertedrrirr .line 26w to .-supplement-lthe pressure t:difierentialrexisting' 'between l-theiinleti-ofwliner-2r3-rand'rthe sexitxofr line I $6,; or a steam :ejecton-may be inserted:.-.at "ltlie? junction. of ."lines :23 and; 25,} with: the ."coke being; inutrodncedx into-I the: .low, pressure; ,zone; oflthe-wenturi.

It-"is: desirab1e in some applications to elutriateorrotherwwise: :classifysthe jet=:attr-iter-. product, i. e., the'irnpacted --.:coke. Thus -a cyclone separator,-or..a tdenser or idilute raphase: "elutniator musing extraneous v, gas and/or 1 the lga's usedrin:thegijet grinder,:camhve inserted. in line 26. {This is desirable in: that the coarsetraction of the; ;jet.iattriter product will be segregated for recycle to the attriter. It has:beenzfoundothat less power his required? to obtain a given size reduction on recycledtcoke particles as compared to fresh particles. Itfis' to' be "understood-that-the=coke fe'ed to; the "attriter may also be-obtained irornrthe lower portion of "the standpipe-of--line--19--as---the-obke -will exi's'tv-u'n'der a relatively high pressure, :comparablecto the pressure ob- .tainedtin the standpipe of line 18. As this .coke. from {the burner is at a'higher temperature, this willgavoid the normal'heatload imposed on the cokerbecause the jet attriter product will be returned to the coker at about the temperature of the coker. Further, in some applications, it may be desired to supply coke to the attriter through a pressurizing standpipe other than those used to circulate coke between the coker and burner. If an extra standpipe be used, it can be of sufficient height to provide a high fluistatic pressure. The use of such an extra standpipe is particularly desirable when wbOflCI I fuelris produced .ztby. other :attriter, .as hereinafter described.

tQther similar-variations?of athe processing sequence ofthis invention will"het-appanentvto those; skilledfi-in the; tart; .zSuitable instrumentation mayube mused-in athe practice. of this; invention without; departing from -.the sspirit thereof.

*Withgparticularrreferencer to.:Figure II; and :III, ;a preiferredrrjetzattritioni mechanism suitable for musein the .ipractice rofthisuinvention will be described. A channelshaped: target surface. 30=impositionedwithin: the :attriter :vesselsi The coke zrpartioleszia long with the conveying -;steam-;areaadrnitted iinto vessel :3 3 through an acceleration ;corrdnit tube ':or':tube;-31; 'Theuaccelerationtube is deitachably: mounted in 2a 1' radial position 1 in attriter vessel .-3:by-flanged:nozzle 542 .a-ndsteritninates in spaced: relation- -;ship s to". the target; surface :30: Thexspacing' of the tube fromf/the target hasmot-tbeen found-".tozzbe critical. For commercial size pipe iof about vzlrto :8':inchesrdiameter; :an :accelerationi'tube'of about 1?. to 'eGf'feet longscan be used. @A' Z i foot long tube has' been found .to :be an optimum length and is preferred; fAsfthetube increases in diame- 'ter, longer lengths maybe used.

There is inserted "in =line 25', that conveys the high veloc'ity-partieles to the jet 'attriter, -a spool piece 32. "This spool 'piece is read ily replaceable. By inserting various lengths,.the'spacinga-of the acceleration tube-to the target surface can -be-'-read'ily varied. This also allows' 'removal and" inspection "of the acceleration tube and'all'ows the insertionofaccelbration tubes of 'different l'eng ths and internal diameters. The use of this spool piece also-permits the jeta-tt'rition mechanism to "berea'dily adapted to '--widely varying operating conditions.

The particular design-of target-30*is another feature 'of this' invention. The "narrow elongated *shape of the "target'permi-ts the use of"a-relativelysmall'aperture in the attriter drum for inserting the target. This-'perrnitst'he use ofrelativelyinexpensive manholesin the "drum to withstand the' pressure. The channel-shape of the target is particularlyadvantageous in that it provides for'maxi- "rnum'andeificientimpacting of the coke particlw This as'"indicated'by"directional lines 33; Other elongated target-shapes can, however, be'usedin'the'practice of this invention, i-ncludingfiat plates and bars. Other forms of "multiple collision-targets may also be used.

"The 'impactedfparticles flowdownwardly through the 'attriter vessel and are removed fromthe vessel through outlet '26, the accelerating-gas being-used to eonveythe particles;

A specialfeature or this invention is'that-the target surface 30 is made to movetransverselyto the axis of the-acceleration tube insuch *a'mannerr that 'a' large target "surface "is available. This allows maximum-continued useofth'e jet attriterby 'minimizing'cessation of operation to replace thetarget "and also promotes the e'fli ciency bf 'gtiliding. "Ithas' been 'discovered'that-even with the best-alloy: steelsavailable; the targetwear rate is about 05001 to 'Oi008 l-b./ton of 'se'ed coke"product produced. 'It' l1a'salso been discovered-thatmovement of the target surface is desirable in that it inhibits the formation of concave target-surfaces. When-a concave-surfaceis 'presented?toltherhighwelocity stream, attrition efliciency fd'ecreases becausethe :impacted particles" rebound in war'dly and form a cushion. Also it is probable that a concave. .surface.allows:oblique impact of the particles such that the energy of :the particlesfi's, only p'artlydis'si- ,pated on the initial impact. -I-t--is--tobe appreciated,

therefore,:;that%this feature offa movable target-isessential i to practical operation of the-jet-attr-iter.

the axis of acceleration tube 31 substantially parallel to the axis of accelerating vessel 3. This motion may, of course, be imparted by manual or mechanical means. Thus an air or electric motor driven worm gear may be used to position the target surfaces. As shown, however, a manual system is used to position the target. A mounting conduit 35 is superposed upon attriter vessel 3. A support bracket 36 is affixed to the mounting conduit and supports a drive shaft capable of reciprocating motion. The drive shaft 37 is afl'ixed to one end of the target member and passes upwardly through the upper portions of the mounting conduit. A sealing arrangement, i. e., a stufling box 38, is used to secure a substantially gas-tight seal between the moving driving shaft and the stationary parts of the attriter. The upper portion of the driving shaft is threaded. The threads engage a crank or handwheel 39, the handwheel being used to impart the desired motion to the drive shaft. There is shown a simple instrumenting device to indicate the position of the target surface relative to the acceleration tube. The indicator consists of a pointer 40 afiixed to the driving shaft and a prepositioned, marked plate 41.

The following example is given as a specific illustration of this invention, but the invention is not to be limited thereby. A fiuid coker similar to the one depicted in Figure I may operate at a coking temperature of950 F. with a pressure in the solids disengaging space, before the cyclones, of 11 p. s. i. g. A coke inventory of 70 tons may be used. The burner temperature may operate at 1125 F. The coke circulation rate to the. burner is, under these conditions, about 4.3 tons/minute. With such size of equipment, the fresh feed is introduced into the coker at the rate of about 3800 B/SD, if the feed has a preheat of 700 F. and inspections of 1.9 API gravity and 30 wt. percent Conradson carbon.

For this feed, approximately 240 tons of coke/ day is produced and 197 tons per stream day is removed as net coke product.

In the standpipe conveying the coke from the fluid coker to the burner, at the point Where the attriter feed is withdrawn, there exists a pressure of approximately 30 p. s. i. g. and the coke-gas suspension has a temperature of 950 F. and a density of 45 lbs/cu. ft. To maintain the balance of coke particle, number and size distribution, approximately 350 tons/day is circulated to the jet attriter. admixed with the coke sent to the attriter/lb. of coke. With an acceleration tube having an I. D. of 2.32 inches and a length of 2 feet, the maximum velocity of the coke particles is 200 ft./second and the gas velocity is 600 a ft./second with a pressure drop of about 15 p. s. i. over the tube. The spacing of the acceleration tube from the target surface is about 6 inches with a target of 10" x 5" channel, 1 thick. The impacted coke is circulated from the attriter at a density of about 0.5 lb./cu. ft. and a velocity of about 60 ft./ sec.

For the above specified conditions, the size and size distribution of the various coke streams is given in the following table I. The table indicates the size of the circulating coke streamin the system (which includes a feed to the attriter vessel), of the product produced by the attriter, and of the net product coke removed from the process. The net process coke is classified so that only relatively coarse material is removed as product.

Table I Circulating Attriter Net Wt. Percent Smaller than- Coke Product Product of Process 800 microns... 99 100 97 400 microns. 95 98 91 295 microns. 81 84. 5 55 246 microns. 46. 54. 0 25 175 microns- 12. 0 25. 7 147 microns..- 6. 5 14. 5 3 74 microns 0. 3 2. 3 0

Approximately 2 S. C. F. of 90 p. s. i. g. steam is i An attractive alternative method of practicing this invention is to operate the jet attriter at high severities to produce a relatively fine attrited product. The finer portion of the attrited material can thenbe removed as net product. In this way, a coke product is produced that is suitable as a fuel in boilers or furnaces. Thus sufficient steam may be used to accelerate the coke particles to relatively high velocities in the range of 1000 f./s., to 2000 f./s., e. g., 1500 f./s. This will produce an attriter product having a substantial portion of material smaller than about 200 mesh. If high severity grinding be practiced, then the attriter product would be classified as by elutriation, cyclone separation, screening, etc., to attain this fine size material as net product coke of the process. The intermediate size fraction from the attriter can be circulated to the coker as seed coke and as a further alternative the coarser material may be recycled to the attriter for further treatment.

Having described the process and apparatus of this invention, what is sought to be protected by Letters Patent is succinctly set forth in the following claims.

What is claimed is:

1. Apparatus for the size reduction of particulate coke which comprises an attriter vessel adapted to contain a movable targetand having an outlet at the bottom for the discharge of comminuted coke, an elongated channelshaped movable target member positioned within said vessel, an acceleration conduit terminating in spaced relation to said target member for admitting a high velocity coke-gas suspension into said vessel in the form of a confined stream, said acceleration conduit being radially positioned in said vessel in such a manner that said confined stream strikes substantially perpendicularly the inner bottom surface of 'said target member, positioning means operativelyconnccted to said target member for positioning said target member transversely to the axis of said acceleration conduit, and mounting means for detachably mounting said positioning means on the top of said vessel.

2. The apparatus of claim 1 wherein said positioning means includes a manually operated shaft attached to said target member.

3. Apparatus for the comminuting of particulate solids which comprises, in combination, an elongated cylindrical attriter vessel with a bottom outlet for ,the discharge of comminuted solids, a relatively narrow elongated mov able target positioned within and parallel to the axis of said vessel, an acceleration conduit radially positioned on said vessel terminating in longitudinal spaced relation along the axis of said acceleration conduit to said target for admitting a confined high velocity solids-gas stream substantially perpendicularly to said target positioning means operatively connected to said target for positioning said target transversely to the axis of said acceleration conduit, and mounting means for detachably mounting said position means on the top of said vessel.

References Cited in the file of this patent UNITED STATES PATENTS 269,741 Taggart Dec. 26, 1882 1,121,631 Hupp Dec. 22, 1914 2,443,714 Arveson June 22, 1948 v FOREIGN PATENTS 401,184 Germany Aug. 26, 1924 433,034 Great Britain Aug. 7, 1935 

